The present invention relates to pneumatic suction devices primarily intended for removing slowly movable material from enclosed storage spaces such as ships' holds, of the kind in which a suction pipe secured to a pivotable arm and having a supply of air arranged to be fed to its suction aperture which is located at its lower end, and is provided with peripherally distributed driven devices for loosening the material. Hereinafter, suction devices of this kind will be referred to as "of the kind described".
It is known that lossening or stirring tools may be made to revolve around the axis of a suction pipe of the kind described, one such device being described in German Patent Specification No. DE-AS 2,055,690. However, in that particular device it is difficult if indeed possible, to extract sluggish materials, e.g. tapioca, by suction from storage spaces, in particular from ships, since steep walls formed in the materials cannot be caused to collapse even by means of pivoting or otherwise movable nozzles at the pipe end. In another case, German Specification No. DE-AS 2,105,143, a double-walled suction head turns around the axis of the suction pipe together with radial conveying tools, so that a considerable torque is thereby applied to the suction pipe and this arrangement is consequently appropriate only for fixed installations, but is not suitable to be positioned on a pivotable arm comprising a freely suspended suction duct for removal by suction of materials from ships in particular.
Particular difficulties arise in all known arrangements if no more than one or two tools engage sideways in the material which is to be conveyed, since the torque or torques cannot be balanced.
It is an object of the invention to reduce or substantially eliminate turning moments applied to a suction pipe of the kind described by loosening tools or at an event to reduce them to a minimum in special cases which remain to be dealt with. It is another object to enable the suction aperture to be displaced vertically downwards as well as sideways into steep walls of the material which is to be conveyed whilst it is being loosened.